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1
Content available Generalized Oberst beam method for measuring viscoelastic parameters of layered composite components
Dobrucki A., Bolejko R., Nieradka P., Klimek A.
Archives of Mechanics
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2023
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Vol. 75, nr 1-2
27--52
EN
This paper proposes two new methods of measuring the viscoelastic parameters of materials. The methods are based on the composite beams’ resonant frequencies measurement. The Young moduli and loss factors of the components are determined by measuring the frequency response of a composite beam twice, each time with different layer thickness ratios. A system of two equations is obtained, from which Young’s moduli of the composite components are calculated. Similarly, two obtained equations determine the loss factors. The results obtained by the proposed methods are compared with those obtained by standard methods and then validated by experiments and FEM simulations. It was noted that the developed models, as well as the standard ones, are highly sensitive to the precision of the samples (material trimming and the way of joining the composite elements). The proposed methods prove to have an advantage over the standard ones in the matter of more frequent measurement criterion fulfilment. The acknowledged criterion represents the existence of a sensible solution insensitive to measurement errors. This criterion, which assures that the results are not prone to errors (for example negative loss factors) is met in 100% of cases in one of the methods, compared to 65% for standard methods.
2
Content available Sound-Absorbing and Insulating Enclosures for Ultrasonic Range
Dobrucki A., Żółtogórski B., Pruchnicki P., Bolejko R.
Archives of Acoustics
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2010
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Vol. 35, No. 2
157-164
EN
The physical phenomena occurring in sound-absorbing and insulating enclosures are subject of the present paper. These phenomena are: absorption in air and by the sound-absorbing material covering the walls and the coincidence effect. The absorption in the air can be neglected in small size enclosures for low ultrasonic frequencies (20–30 kHz). The coincidence plays a role in decrease of the sound insulation, however the main role play the leaks. The boards made of ceramic fibers have been chosen as the optimal sound-absorbing material. They are dense and have deeply porous structures. The enclosure for insulation of 20-kHz noise produced by a welding machine has been designed and manufactured, and reductions of 25 dB of peak and Leq levels have been achieved.
3
Content available remote FEM amd BEM computing costs for acoustical problems
Bolejko R., Dobrucki A.
Archives of Acoustics
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2006
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Vol. 31, No. 2
193-212
EN
FEM and BEM computing costs are compared for acoustical problems. The cost analysis was carried out for bounded areas of simple shapes for objects with acoustical losses (e.g. with sound absorbing materials). BEM's variational-collocative scheme (DBEM) and its variational scheme (IBEM) were considered. Computing costs were calculated, taking into account main matrix composition costs and main system of equations solution costs. The costs were calculated for the type of adopted discrete elements and the order of quadrature used. Analytical relations for calculating main matrix composition costs for BEM have been derived. The analysis shows that FEM computing costs can be lower than BEM computing costs. Moreover, BEM computing costs are strongly dependent on the order of the quadrature used. The presented results provide a basis for the choice of the most cost-effective method depending on the size of an acoustical problem.
4
Studio nagrań Zakładu Akustyki Politechniki Wrocławskiej. Ochrona przeciwdźwiękowa
Bolejko R., Mazurkiewicz M.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
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2004
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Vol. 85, nr 29
11-18
PL
W pracy przedstawiono zmierzone wartości tła akustycznego i izolacyjności akustycznej wybranych przegród budowlanych w studiu nagrań Zakładu Akustyki. Zmierzone wartości porównano z wartościami zalecanymi dla tego typu pomieszczeń. Omówiono przyczynę powstania stosunkowo dużych zakłóceń przedostających się z sal lekcyjnych znajdujących się nad pomieszczeniami studyjnymi. Podano praktyczne aspekty wykorzystania studia nagrań ze względu na istniejącą izolacyjność akustyczną badanych pomieszczeń.
EN
The paper describes the influence of the recordings enhancement for the recognition of speaker voice. The experiments were carried out for various noise levels with its influence on speaker recognition with usage of the available signal enhancement system.
5
Studio nagrań dźwięku zakładu akustyki Politechniki Wrocławskiej. Wybrane zagadnienia akustyki wnętrza
Bolejko R., Kozłowski P.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
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2003
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Vol. 84, nr 28
53-58
EN
In the paper selected room acoustics aspects of the new recording studio of the Acoustics Department at the Wroclaw University of Technology are presented. Measured normal modes distribution, early reflections and reverberation time are discussed. Designing rules of the optimal room dimensions are outlined as well.
6
Studio nagrań dźwięku Zakładu Akustyki Politechniki Wrocławskiej. Wybrane zagadnienia technologii studyjnej
Kozłowski P., Bolejko R.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
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2003
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Vol. 84, nr 28
47-52
EN
Technology at the example of new made surround recording studio is presented in the paper. Wiring system and connection topology are shown. Kinds of signals, connectors and ways of wiring are listed. Benefits of using digital technology are discussed. Plan for listening monitor's placement is shown. Requirements and solutions about mixing console, signal processors and studio furniture are written.
7
Wpływ kształtu na pole akustyczne wewnątrz przestrzeni ograniczonej
Bolejko R.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
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2001
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Vol. 83, nr 27
45-50
EN
In the paper the influence of shape on the acoustic field inside enclosure without damping is presented. Two-dimensional shapes: rectangular, rectangular with one inclined side, regular triangle, regular pentagon and regular hexagon were investigated. Irregularity of acoustic pressure in enclosure is evaluated in terms of mean value and standard deviation, whereas frequency distribution is evaluated in terms of Bolt criterion. Shape has a strong influence on the irregularity of acoustic pressure and frequency distribution of the normal modes in enclosure. Regular triangle, pentagon and hexagon shapes show lower mean value of acoustic pressure and worse irregularity of acoustic pressure and frequency distribution as compare to rectangular one. Inclining one side in rectangular shape up to 10° does not affect on the irregularity of acoustic pressure whereas improves frequency distribution of the normal modes. Father inclining is not favorable
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